Integrated method for controlling diesel engine emissions in CRT-LNT system

ABSTRACT

A method for controlling diesel engine emissions is disclosed. The diesel engine&#39;s exhaust system has a NO x  oxidation catalyst, a diesel particulate filter (DPF), and a lean NO x  trap (LNT). The DPF is monitored to determine the need for regeneration. The LNT is monitored to determine the need for regeneration or desulfurization. A fuel injector is used to inject fuel upstream of the LNT under certain conditions, and a bypass may be used to bypass exhaust around the oxidation catalyst to provide richer or hotter exhaust to the LNT.

RELATED APPLICATION

[0001] This application is a divisional application of application Ser.No. 09/961,442 filed Sep. 24, 2001, entitled “Integrated System forControlling Diesel Engine Emissions” which is a continuation-in-partapplication of application Ser. No. 09/339,080 filed Jun. 23, 1999,entitled, “Multiple Stage Aftertreatment System”, now U.S. Pat. No.6,293,096.

TECHNICAL FIELD

[0002] This invention relates generally to emission control for internalcombustion engines, and more particularly to a control system for dieselengines that provides integrated control of engine and post-combustionemission control devices, the latter including both DPF and LNT devices.

BACKGROUND OF THE INVENTION

[0003] New emission limits call for major reductions in oxides ofnitrogen (NO_(x) ) and particulate matter (PM) emissions from dieselengines. Engine manufacturers have developed systems for exhaust gasrecirculation (EGR), and diesel particulate filters (DPF) to achieve lowNO_(x)/PM emissions. The use of DPFs has been found to reduce PM belowthe stringent requirements of the new emission standards proposed forthe 2005 through 2010 time frame. However, NO_(x) emissions are stillsix to eight times higher than the proposed standards for model year2007.

[0004] To achieve the target NO_(x) emission levels, new post-combustiondevices are being experimented with. These devices include selectivecatalytic reduction (SCR) using urea or ammonia as reductant, and leanNO_(x) traps (LNT) (otherwise known as NO_(x) adsorbers) usinghydrocarbon as reductant. Although SCR systems have been used instationary applications for several years they are now being developedfor the mobile fleet with good success. However, greater NO_(x)reduction than SCRs can deliver is still hoped for and the LNT systempromises to achieve the desired NO_(x) conversion efficiency.

SUMMARY OF THE INVENTION

[0005] The invention is directed to methods and systems for controllingdiesel engine emissions. In all embodiments, the diesel engine's exhaustsystem has at least a diesel particulate filter (DPF) and a lean NO_(x)trap (LNT). The DPF may be one of two types: a first type that uses acatalyzed soot filter or a second type that uses a continuouslyregenerated trap. In either case, the LNT is monitored to determine theneed for regeneration or desulfurization. In the former case, thecatalyzed soot filter is also monitored to determine the need forregeneration. A fuel injector is used to inject fuel upstream of the LNTunder certain conditions, and a bypass may be used to bypass exhaustupstream of the LNT to provide richer or hotter exhaust to the LNT. Thesensor outputs and controls for providing the appropriate heat or fuelmix for regeneration and desulfurization may be controlled withenhancements to existing engine control circuitry.

[0006] Features of the invention include the capability of integrationof engine controls with control of post combustion emission controldevices. Intake throttling, existing EGR systems, and post-combustioninjection can be used, alternatively or in combination, for the purposeof regenerating the LNT. Existing EGR can be used to reduce NO_(x)without adversely affecting the ability to maintain low PM emissions. Aportion of the exhaust can be diverted to assist in creating astoichiometric air-to-fuel ratio at the inlet of the LNT to facilitateregeneration. Overall, the system performs all of the above while notaffecting drivability.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]FIG. 1 illustrates a first embodiment of a multiple stageaftertreatment system.

[0008]FIG. 2 illustrates a second embodiment of a multiple stageaftertreatment system.

[0009]FIG. 3 illustrates a NO_(x) and PM reduction system having aCSF-LNT unit in the exhaust path.

[0010]FIG. 4 illustrates a NO_(x) and PM reduction system having aCRT-LNT unit in the exhaust path.

DETAILED DESCRIPTION

[0011] Tri-Stage Aftertreatment Device

[0012] U.S. patent application Ser. No. 09/339,080, entitled “MultipleStage Aftertreatment System” to Khair, et al., now U.S. Pat. No.6,293,096, and assigned to Southwest Research Institute, describes anaftertreatment system for reducing the amount of nitrogen oxide andparticulate matter in engine exhaust gases without the need for electricheating elements to increase the temperature of the exhaust gas toperiodically regenerate the particulate filter. The aftertreatmentsystem does not require the injection of additional fuel in eachcylinder of the engine to provide additional necessary hydrocarbon toreduce the NO_(x) to N₂ (nitrogen). It has an internal bypass for theNO₂ trap to control the rate of NO₂ directed to the carbon trap.

[0013] A first preferred embodiment of the aftertreatment system isgenerally indicated by reference numeral 8 in FIG. 1, and effectivelycombines the functions of a CRT (catalytically regenerated trap), a LNT(lean NO_(x) trap), and a carbon trap in a single system for thereduction of both NO_(x) (nitrogen oxides) and PM (particulate matter)emissions. The aftertreatment system 8 is particularly adapted tooperate in lean air-fuel ratio engines, such as diesel engines, and usesthe excess oxygen present in the exhaust stream of such lean burnengines to reduce the amount of NO_(x) and carbonaceous particulatematter discharged into the atmosphere. The main elements ofaftertreatment system 8 are a first stage 10, a second stage 20, a thirdstage 30, and a hydrocarbon fuel injector 40 interposed between thefirst stage 10 and the second stage 20.

[0014] The first stage 10 has an inlet 12 which is adapted to receiveexhaust gases discharged from an internal combustion engine, such as adiesel engine (not shown). Typically, the exhaust gas from a dieselengine contains various oxides of nitrogen (NO_(x)) and particularly NO(nitric oxide) and NO₂ (nitrogen dioxide), as well as HC (hydrocarbons),CO (carbon monoxide), CO₂ (carbon dioxide), PM (particulate matter), andother products of the combustion process. The first stage 10 of theaftertreatment system includes an oxidation catalyst 14, preferably anoble metal such as platinum or palladium. The catalyst 14 oxidizes theNO in the exhaust gas stream, in the presence of the catalyst, to NO₂.This reaction is represented by Formula 1:

1) NO+½O₂→NO₂

[0015] Thus, NO₂ (nitrogen dioxide) is formed and is carried into thesecond stage 20 of the aftertreatment system 8.

[0016] The second stage 20 of the aftertreatment system 8 includes afirst portion 22 and a second portion 24. The first portion 22 containsa lean NO_(x) trap (LNT). The lean NO_(x) trap stores NO₂ under leanfuel-air mixture (i.e., oxygen-rich) engine operation, then reduces thestored NO₂ to N₂ and O₂ under rich fuel-air conditions. In most dieselapplications, rich fuel-air conditions do not frequently occur duringnormal over-the-road or other relatively steady state operation. Theportion of the NO₂ stored in the LNT 22 of the second stage 20 combineswith the supplemental HC provided by the periodic injection ofsupplemental HC (hydrocarbon fuel) upstream of the second stage 20 toform N₂, H₂O and CO₂. The reduction of NO₂ in the second stage isrepresented by Formula 2:

2) NO₂+HC+O₂→N₂+H₂O+CO₂

[0017] With continued reference to FIG. 1, the hydrocarbon fuel injector40 is in fluid communication with a source 42 of pressurized hydrocarbonfuel, for example diesel fuel such as that used in the normal operationof the engine. The reduction conversion efficiency of NO₂ to N₂ and O₂in the second stage is typically somewhat less than 100% and therefore,some NO₂ is expected to escape the LNT 22 and pass on to the third stage30. Another portion of the NO₂ formed in the first stage 10 bypasses theLNT 22 of the second stage by being directed through the second portionbypass 24 of the second stage 20. The size of the bypass 24 can bereadily determined by experimentation for specific applications toensure good NO_(x) and PM emission reduction.

[0018] The third stage 30 of the aftertreatment system 8 in the firstembodiment of the present invention includes a carbon trap oxidizer 32such as a ceramic cordierite wallflow trap. In the carbon trap oxidizer32, the NO₂ reacts with carbon in the trap and forms CO₂ and N₂. Thus,the unconverted NO₂ from the first portion 22 of the second stage 20, aswell as bypassed NO₂ passing through the second portion 24 of the secondstage 22, is reduced to nitrogen and CO₂ and is represented below byFormula 3:

3) 2NO₂+2C→N₂+2CO₂

[0019] Thus, in the first stage 10 of the multiple stage aftertreatmentsystem 8, NO resulting from the diesel combustion process combines withexcess oxygen in the exhaust gas stream to form NO₂, aided by thecatalyst 14 in the first stage 10. In the second stage 20, a lean NO_(x)trap stores the NO₂ formed by the oxidation catalyst 14 of the firststage 10. The stored NO₂ then combines with supplemental HC, injected bythe injector 40 to form N₂, H₂O, and CO₂. Unconverted as well asbypassed NO₂ then proceed to the carbon trap oxidizer 32 of the thirdstage 30, where NO₂ is reduced to N₂ and carbon is oxidized to CO₂, NO₂is stored in the LNT portion 22 of a second stage 20 as long as theexhaust is lean (oxygen-rich). As the LNT portion 22 reaches its NO₂storage capacity limits, the fuel injector 40, positioned just upstreamof the LNT portion 22, delivers supplemental hydrocarbon in the form ofdiesel fuel, thereby reducing NO₂ to N₂.

[0020] Switching from the NO₂ storage mode to the reducing mode ispreferably controlled by the use of a NO_(x) sensor 50 positioned in theexhaust downstream of the second stage 20, and preferably between thesecond stage 20 and the third stage 30. The NO_(x) sensor 50 senses theNO_(x) content of the exhaust stream and is thereby capable ofindirectly detecting engine load. The NO_(x) sensor 50 delivers anelectrical signal 52 to a programmable controller 54 which conditionsthe electrical signal 52 and controls the operation of the hydrocarbonfuel injector 40. Thus, fuel can be controllably injected into theaftertreatment system 8 under desired engine operating conditions toenhance the performance of the LNT portion 22 of the second stage. Analternative to sensing NO_(x) is measuring exhaust gas temperature foruse as an indicator of engine speed and load. NO_(x) formation in dieselengines is a function of engine temperature, generally increasing as thecombustion temperature increases, and thus it can be inferred thatNO_(x) formation is taking place at a high rate under high temperatureengine operating conditions. At such times, supplemental diesel fuel canbe injected to reduce the NO_(x) emissions. It is desirable that thefuel used for engine operation be a low sulfur fuel to prevent damage tocatalysts in the system.

[0021] A second embodiment of the aftertreatment system is indicated byreference numeral 108 in FIG. 2. In the second embodiment, the leanNO_(x) trap and carbon trap are reversed with respect to their positionsin the first embodiment, but still effectively produce the samedesirable reduction in both NO_(x) and particulate matter in the exhaustemission stream. As in the first embodiment, the first stage 110includes an oxidation catalyst 114 positioned just downstream of aninlet 112. The catalyst 114 oxidizes the NO in the exhaust stream in thepresence of the catalyst, to NO₂. Thus, the reaction that takes place inthe first stage of the second embodiment is the same as that shown inFormula 1 above.

[0022] In the second embodiment, the second stage 130 includes a carbontrap oxidizer 132, such as a ceramic cordierite wallflow trap. In thecarbon trap 132, NO₂ in the gas stream discharged from the first stagereacts with the carbon component of the carbonaceous particulate matterin the exhaust gas stream, reducing at least a portion of the NO₂ to N₂and simultaneously oxidizing the carbon to form carbon dioxide (CO₂).The amount of NO₂ reduced is dependent upon the amount of carbonpresent, and therefore, the reduction of NO₂ to N₂ may not be 100%. Thatis, the exhaust gas stream discharged from the second stage 132 usuallywill contain both reduced NO₂ (N₂) and oxidized carbon (CO₂) as well assome residual nitrogen dioxide (NO₂), as represented below by Formula 4:

4) 2NO₂+2C+NO₂→N₂+2CO₂+NO₂

[0023] With continued reference to FIG. 2, the third stage 120 includesa lean NO_(x) trap (LNT) 122. The gas stream emitted from the secondstage 130, containing nitrogen, carbon dioxide and a remaining portionof nitrogen dioxide passes through the third stage 120. The third stagelean NO_(x) trap is arranged to store the remaining portion of thenitrogen dioxide discharged from the second stage, and with the additionof a supplemental hydrocarbon fuel, reduce the stored nitrogen dioxideto nitrogen, water in a gaseous state, and carbon dioxide, and dischargea gaseous stream from the multiple stage aftertreatment system 108 thatconsists essentially of nitrogen, water and carbon dioxide. Thisreaction is represented above by Formula 2.

[0024] Aftertreatment system 108 has a hydrocarbon fuel injector 140that is positioned between the second stage 130 and the third stage 120at a position adapted to controllably inject selected amounts ofhydrocarbon fuel, from a pressurized source 142, into the gaseous streamdischarged from the second stage 130, prior to the gaseous stream beingreceived by the third stage 120. As described above, the lean NO_(x)trap 122 stores the remaining portion of the NO₂ then combines thestored NO₂ with supplemental HC, injected by the injector 140 to formN₂, H₂O and CO₂. NO₂ is stored in the lean NO trap portion 122 of thethird stage 120 when the exhaust is lean (oxygen-rich). As the leanNO_(x) trap portion 122 reaches its NO₂ storage capacity limits, thefuel injector 140, positioned just upstream of the lean NO_(x) trap 122delivers supplemental hydrocarbon (HC) in the form of diesel fuel,thereby inducing NO₂ reduction to N₂.

[0025] Switching the NO₂ from the storage mode to the reducing mode maybe controlled, as described above, by the use of a NO_(x) sensor 150positioned in the exhaust downstream of the third stage 120. The NO_(x)sensor 150 senses the NO_(x) content of the exhaust stream and isthereby capable of indirectly determining engine load. The NO_(x) sensor150 delivers an electrical signal 152 to a programmable controller 154which conditions the electrical signal 152 and controls the operation ofthe hydrocarbon fuel injector 140. Thus, fuel can be controllablyinjected into the aftertreatment system 108 under desired engineoperating conditions to enhance the performance of the lean NO_(x) trapportion 122 of the third stage 120.

[0026] The multiple stage aftertreatment devices described above combinethe functions of a catalytically regenerated trap (CRT) with a leanNO_(x) trap (LNT) in a single system for the reduction of both NO_(x)and PM emissions. This effectively maximizes the common features of bothsystems, such as a noble metal catalyst and its NO₂ formationcapability.

[0027] Integrated Systems for Diesel Engine Control

[0028] The following description is directed to the integration of anemission control system consisting of a diesel engine equipped with anEGR and intake throttle, and capable of post-injection, withpost-combustion exhaust emission control devices. The emission controldevices in the exhaust are a DPF, LNT, supplemental fuel (reductant)injector, and a bypass valve. The tri-stage concepts discussed above areintegrated into the overall engine emission control system.

[0029] Two categories of control systems are discussed, each using adifferent DPF system. A first system uses a Catalyzed Soot Filter (CSF),whereas a second system uses a Continuously-Regenerated Trap (CRT™). Thefollowing description describes two systems: a CSF-LNT system and aCRT-LNT system. Both systems have at least seven features that interactto facilitate control of the regeneration and/or desulfurization of theemissions components:

[0030] 1) Intake air throttling

[0031] 2) A venturi used to enhance EGR flow

[0032] 3) Cooled EGR System

[0033] 4) Post combustion fuel injection (in-cylinder and/or in exhaust)

[0034] 5) A bypass valve in the exhaust stream to direct flow duringdesulfurization

[0035] 6) Placement of the supplemental fuel injector in the exhaust

[0036] 7) Embedded software that contains integration and control logic

[0037] CSF-LNT Configuration and Control

[0038]FIG. 3 illustrates the CSF-LNT system 300, which has the enginecontrols noted above (i.e., EGR line 301, EGR valve 302, EGR cooler 303,intake throttle 304, intake venturi 305, electronic engine controls322). The exhaust system has a CSF 310, an LNT 311, a bypass valve 313,and a fuel injector 317, as well as CSF pressure and temperature sensors330 and 333, and LNT NO_(x) sensors 331 and 332. Sensor 330 monitors CSFdP (pressure drop), and sensors 331 and 332 monitor NO_(x) levels beforeand after the LNT 311.

[0039] As explained below, the monitoring sensors 330-333 are used todetermine the need for regeneration of both systems. Their outputsignals may be delivered to engine controller 322, which performsappropriate algorithms for implementing the regeneration anddesulfurization described below, including control of various engine andexhaust devices so as to enhance conditions for regeneration anddesulfurization.

[0040] CSF 310 may be any device that acts as a particulate filter,wherein part or all of the surface of the filter is “catalyzed” (i.e.,coated with catalytically active materials). NO in the exhaust isoxidized to NO₂ on the catalyzed surfaces of the filter, and the NO₂then oxidizes the carbon trapped on the filter. For the rate ofregeneration to exceed the rate of trapping in the CSF 311 (i.e., theCSF can clean out any accumulated soot particles), the temperature mustgenerally exceed 380° C. If long periods of operation are performedbelow this temperature (for example sustained idle or light loadoperation), it may be necessary to artificially elevate the temperatureof the CSF 310 for a period of time to clean it.

[0041] A bypass valve 313 is incorporated upstream of the CSF 310 toallow a small portion of the exhaust to be routed around the CSF 310,via a bypass line 315, and reintroduced into the exhaust upstream of theLNT 311. A supplemental fuel injector (SFI) 317 is located in theexhaust between the CSF 310 and LNT 311 to allow for injection ofadditional fuel to supplement the air-to-fuel ratio of the exhaustentering the LNT 311. All of these systems are controlled from theelectronic control module (ECM) 322.

[0042] Under normal operation, all of the engine exhaust passes firstthrough the CSF 310 and then through the LNT 311. The CSF 310 trapsinsoluble particulates and oxidizes volatile organic particulates. Inaddition, if the temperature is high enough (over 380° C.) some of theNO₂ generated by the CSF 310 removes carbon particles already trapped inthe CSF 310. Excess NO₂ from CSF 310 is stored on LNT 311. The exhaustflows enters the LNT 311, where any remaining NO is oxidized to NO₂. TheNO₂ then adsorbs on the surface of the LNT.

[0043] When the CSF 310 differential pressure indicates thatregeneration is needed, and the temperature of the CSF 310 is not at therequired level, the exhaust temperature is increased using controlstrategies programmed into the ECM 322. This may be done using intakethrottle 304, increased EGR rate, or in-cylinder post-combustion fuelinjection while the exhaust valves are open (referred to aspost-injection). Intake throttling or increased EGR rate increases theexhaust gas temperature from the engine 320. Post-injection increasesthe CSF temperature by using the exothermic heat generated by theoxidation of the post-injected fuel. These methods may be usedseparately or in combination, and may be optimized to produce thehighest temperature for the smallest amount of performance and fuelpenalty.

[0044] When NO_(x) monitors at the inlet and outlet of the LNT 311indicate that NO_(x) reduction across the LNT 311 has fallen belowacceptable levels, regeneration and/or desulfurization will be needed.LNT regeneration requires temperatures above 250° C. and astoichiometric or slightly rich exhaust gas air-to-fuel ratio. Iftemperature is not sufficient for regeneration, it may be increasedusing any or a combination of the methods described above for increasingthe CSF temperature.

[0045] To generate the rich exhaust gas air-to-fuel ratio, a variety ofmethods may be used. Intake throttling and increased EGR will generatehigher CO levels in the exhaust. The bypass valve 313 may be used topass a portion of this CO laden exhaust around the CSF 310 (which wouldotherwise oxidize and remove the CO), thus moving the exhaust closer toa rich condition upstream of the LNT 311. Post-injection could also beused to add more fuel into the exhaust, again in conjunction with thebypass valve 313. Some of the post-injected fuel may also make itthrough the CSF (or be partially oxidized to generate CO by the CSF)depending on exhaust gas temperature and flow rate. Finally, fuelinjector 317 may be used to inject additional fuel into the exhaustupstream of the LNT 311 to ensure the rich exhaust conditions needed forregeneration. Any combination of these may be used, and the regenerationstrategy may be optimized to achieve the fastest and most completeregeneration for the least amount of fuel economy and performancepenalty.

[0046] If, after a period of regeneration, the NO_(x) sensors indicatethat NO_(x) reduction across the LNT 311 has still not returned toacceptable levels, then a need for desulfurization is indicated.Desulfurization requires temperatures between 400° C. and 600° C., withhigher temperatures requiring a shorter period of time to completedesulfurization. This increased temperature may be accomplished by anyor a combination of the means described above for the CSF 310. Inaddition, the bypass valve 313 may be used to pass some of the hotexhaust around the CSF 310 and into the LNT 311 in order to prevent someof the heat from being lost to the CSF. Finally, the fuel injector 317may be used to generate heat in the LNT 311 by using the exothermic heatcaused by oxidation of the injected fuel over the LNT itself. Anycombination of these may be used, and the desulfurization strategy maybe optimized to achieve the fastest and most complete desulfurizationfor the least amount of fuel economy and performance penalty.Desulfurization may be halted periodically to check if NO_(x) reductionhas returned to acceptable levels, and can be resumed if the checkindicates more desulfurization is needed. If desulfurization isunsuccessful after several attempts, a problem with the LNT 311 could beindicated.

[0047] Balancing the above-described regeneration and desulfurizationrequirements calls for an integrated control strategy. Areas whereseveral requirements overlap can be exploited to accomplish these taskssimultaneously (e.g., temperature increase episode for CSF regenerationcan also be used for LNT regeneration and/or desulfurization) to reducethe overall fuel economy and performance penalties associated with suchoperation. In addition, episodes where exhaust temperatures and flowrates are ideal for regeneration can be exploited by using any of thesetechniques (e.g., post-injection during deceleration events, to allow abrief period of regeneration without affecting driveability).

[0048] CRT-LNT Configuration and Control

[0049]FIG. 4 illustrates another embodiment of an integrated system, aCRT™-LNT system 400, which has then engine 420 and engine controls notedabove (i.e., EGR line 401, EGR valve 402, EGR cooler 403, intakethrottle intake venturi 405, electronic engine controls 422). Asexplained above CRT 410 is an alternative to the CSF of system 300, andboth devices have a LNT. The configuration of the system 400 is suchthat the bypass control valve 413 is placed upstream of the oxidationcatalyst (OC) 410 a and is configured so as to bypass the OC 410 a. Thenext emissions component in the exhaust flow is the DPF 410 b, followedby the LNT 411. Together the OC 410 a and DPF 410 b make up the CRT™410.

[0050] CRT 410 may be any device that converts NO to NO₂ in a firststep, followed by a wallflow DPF where carbonaceous particulate isaccumulated. LNT 411 may be any device that has an oxidation catalyst tooxidize nitric oxide (NO) to nitrogen dioxide (NO₂), followed by an NO₂trap (usually a base-metal oxide) wherein NO₂ is adsorbed on thesurface. Temperature and pressure sensors 430 and 433 are placed at theDPF 410 b to determine the need for DPF regeneration, and NO_(x) sensors431 and 432 are used to determine the need for regeneration anddesulfurization of the LNT 411. Regeneration and desulfurizationconditions are determined in a manner similar to the methods describedabove in connection with system 300.

[0051] The LNT 411 is periodically regenerated under conditions ofsufficient temperature and stoichiometric (or slightly rich) exhaustair-to-fuel ratio. In addition to regeneration, the LNT 411 is“desulfurized” periodically. This is necessary because sulfur (in theform of sulfur trioxide) adsorbs in the surface of the LNT 411, blockingthe sites used to trap NO₂ and thus reducing the efficiency of the LNT.Desulfurization requires high temperature (400° C. to 600° C.) for asustained period of time (often several minutes—much more time thanrequired for regeneration), and stoichiometric or slightly richair-to-fuel ratio conditions.

[0052] Referring to FIG. 4, system 400 operates in the following manner.The OC 410 a converts NO to NO₂ in the exhaust stream. The exhaust thenflows through the DPF 410 b, where PM in the exhaust is trapped and thecarbon is reacted with NO₂ to form elemental nitrogen and carbon dioxide(CO₂). Excess NO₂ emitted from the DPF 410 b is stored on the LNT 411,until the LNT is regenerated.

[0053] To integrate the CRT™-LNT system 400, software logic is added tothe engine controller 422 to monitor the system status and to controlthe regeneration/desulfurization of the emissions systems as needed. Forthe LNT 411, NO_(x) sensors 431 and 432 are monitored and theirlocations strategically determined, to develop a strategy for indicatingwhen regeneration of the LNT 411 is required. An additional strategymonitors regeneration frequency and deciphers whether a regeneration ordesulfurization is required. Once the condition forregeneration/desulfurization is met, an engine control strategy is usedto create a rich condition, with adequate carbon monoxide (CO) toinitiate regeneration in the NO_(x) trap. To achieve this goal, intakethrottling (to increase the vacuum across the venturi 405, resulting inincreased EGR) may be used to create a richer in-cylinder air-to-fuelratio (increasing CO in the exhaust), the bypass valve 413 may bepartially activated to prevent the consumption of the excess CO acrossthe OC 410 a, and in-exhaust (or in-cylinder post combustion)supplemental fuel injection (SFI) 417 will be used to further raise COand to increase the exhaust temperature to regenerate the LNT 411.Additional logic may be programmed into the controller 422 to verifythat the duration of regeneration/desulfurization event was adequate toachieve complete regeneration. CO emitted during DPF regeneration willalso help regenerate the LNT 411.

[0054] The control logic also monitors and controls the regeneration ofthe DPF 410 b. For the DPF 410 b, filter pressure drop (dP) and inletexhaust temperature are monitored with pressure and temperature sensors430 and 433. A strategy is developed to determine when regeneration isnecessary. Ideally, the regeneration strategy achieves continuousregeneration through engine management, and avoids cyclic regeneration.The strategy for continuous DPF regeneration involves identifying thebalance point temperature (BPT) (the temperature at which the rate ofsoot accumulation is equal to the rate of regeneration), predicting inreal-time whether the DPF is at or below the BPT, and continuouslyadjusting in-cylinder, post combustion fuel injection characteristics inan attempt to maintain BPT.

[0055] Other Embodiments

[0056] Other aspects, features and advantages of the present inventioncan be obtained from a study of this disclosure together with theappended claims.

What is claimed is:
 1. A method of reducing the amount of NO_(x) andcarbonaceous particulate matter in exhaust from an internal combustionengine, said NO_(x) having nitric oxide as one component thereof, themethod comprising: receiving the exhaust into a first stage, the firststage having a NO_(x) oxidation catalyst adapted to oxidize the nitricoxide to nitrogen dioxide and discharge a gaseous stream containingreduced exhaust; positioning a second stage in fluid communication withsaid first stage and adapted to receive said gaseous stream from saidfirst stage, said second stage having a carbon trap adapted to storecarbonaceous particulate material contained in the gaseous stream, toreduce a portion of the nitrogen dioxide contained in the gaseousstream, to oxidize the carbon component of the carbonaceous particulatematter contained in the gaseous stream, and to discharge a gaseousstream containing at least nitrogen, carbon dioxide, and any residualnitrogen dioxide; interposing a bypass valve between the engine and thefirst stage, operable to bypass a portion of the exhaust around thefirst stage and into the second stage; positioning a third stage influid communication with said second stage and adapted to receive saidgaseous stream from said second stage, said third stage having a leanNO_(x) trap adapted to store nitrogen dioxide discharged from saidsecond stage and to reduce at least a portion of the nitrogen dioxide byreaction with the carbonaceous particulate matter and to oxidize atleast a portion of the carbonaceous particulate matter; sensing whenregeneration of the third stage is to be performed; and bypassing atleast a portion of the exhaust around the first stage in response to thesensing step.
 2. The method of claim 1, further comprising the step ofinterposing a hydrocarbon fuel injector between the first and secondstages.
 3. The method of claim 1, further comprising the step of sensingdifferential pressure at the second stage to determine the need forregeneration of the second stage.
 4. The method of claim 1, furthercomprising the step of sensing temperature at the second stage todetermine the need for regeneration of the second stage.
 5. The methodof claim 1, further comprising the step of regenerating the second stageby raising the temperature at the soot filter.
 6. The method of claim 1,further comprising the step of sensing NO_(x) reduction across the thirdstage to determine the need for regeneration of the third stage.
 7. Themethod of claim 1, further comprising the steps of regenerating thethird stage by raising temperature at the second stage and providing aricher exhaust gas air-to-fuel ratio.
 8. The method of claim 1, furthercomprising the step of sensing NO_(x) reduction across the third stageto determine the need for desulfurization of the third stage.
 9. Themethod of claim 1, further comprising the step of desulfurizing thethird stage by raising temperature at the third stage.
 10. The method ofclaim 1, further comprising the step of continuously regenerating thesecond stage.
 11. The method of claim 10, wherein the step ofcontinuously regenerating is in response to monitoring the balance pointtemperature at the second stage.